Semiconductor fabrication plants typically handle, process, inspect and measure wafers. One example of equipment used in such processing operations and handling systems is an integrated metrology tool. The term “integrated monitoring tool”, as used herein, refers to a monitoring (e.g., metrology, inspection) apparatus that is preferably physically installed inside a wafer processing tool or attached to it. However, it can also be separated form the processing unit, as necessary. The monitoring tool is usually dedicated to the specific processing unit and wafers are preferably transferred to the tool by a robot. The same robot may serve the processing unit as well. One exemplary process environment uses the NovaScan 2020 integrated metrology tool, commercially available from NOVA Measuring Instruments Ltd. of Rehovot, Israel, and its handling system.
Examples of processing units and buffer stations for use in such process environments are described in U.S. Pat. No. 6,212,961 to Dvir, assigned to NOVA Measuring Instruments Ltd. Rehovot, Israel. The processing unit of U.S. Pat. No. 6,212,961 comprises a processing station for processing one or more wafers, a measuring station for measuring the wafers, a robot for moving the wafers between the processing and measuring stations, a wafer handling system and a buffer station. The wafer handling system operates in conjunction with the measuring station and moves the wafer to and from a measuring location on the measuring unit. The buffer station is associated with the wafer handling system and receives measured and unmeasured wafers thereby to enable the robot to arrive at and leave the measuring station with at least one wafer thereon.
In the prior art, the wafer may be held by some sort of gripping device (e.g., a vacuum gripper), and the wafer handling system takes the wafer from the gripping device to the station where measurements (or other process steps, e.g., metrology or inspection) are carried out.